た

plate i, and thence around the coil of the galvanometer to plate f, across the river again to plate g, and thence to the other pole of the battery R, to complete the circuit.

These experiments were made with different lengths of wire laid along the banks of the canal, and with batteries, the number of elements com

posing which were of different strengths. In the

W

B

FIG. 3.

result it was found that the quantity of electricity which passed from one bank of the stream to the other stood in direct relationship to the size of the plates sunk in the water, as well as to the distance of the plates on the same side of the river from each other. From these and other experiments it was deduced that this distance should be three times greater than that from shore to shore. A greater distance than that did not give any increase of power.

Similar experiments were carried out by Messrs. Vail and Rogers, two of Professor where the distance separating the two circuits Morse's assistants, across the Susquehanna River,

VAIL AND ROGERS

25

was nearly a mile, and with complete success. It is curious to note that, in his communication to the Secretary of the Treasury, Morse remarks that "experience alone can determine whether lofty spars, on which wires may be suspended, erected in the rivers, may not be deemed the most practical."

A full account of these experiments is given in Alfred Vail's American Electromagnetic Telegraph, published in 1845, and reprinted in the Electrical World, June 29, 1895.

CHAPTER II

Wilkins' proposed method of wireless communication with France-Dering's experiments with conduction through water-Lindsay-His electrical researchesProposal to telegraph across the Atlantic-His method -Experiments across the Tay and elsewhere.

THE next worker in the field of wireless telegraphy of whom we have any knowledge is Mr. J. W. Wilkins, whose experiments were begun in 1845. Wilkins was associated for many years with Messrs. Cooke and Wheatstone, the pioneers of electric telegraphy in Great Britain; and in a letter appearing in the Mining Journal, March 28, 1849, he clearly sets forth a method whereby, as he conceived, telegraphic communication might be established between England and France, which the submarine cable had not at that time joined. As this letter, from the suggestions it contains, is of great importance in the history of wireless telegraphy, it will be well to give almost entire the writer's description of the method by which he proposed to carry out his "theory upon which a telegraphic communication may be made between England and France without wires."

"I take for certain," he proceeds-" as experi

WILKINS' SUGGESTION.

27

ments I have made have shown me that when the positive and negative poles of a battery are dipped into or connected with any conducting medium, the electricity around the positive pole is positive, being diffused in radial lines, and the part around the negative pole is negative in radial lines converging toward it, supplying the electricity requisite for the decomposition of the substances composing the battery. This understood, it is evident that when a positive radial line sets out from the junction of the battery with the earth it makes its way to, or is attracted by the nearest negative portion of earth, at last meeting the negative pole of the battery, restoring the equilibrium. From this it appears that the first portion of electricity will pass in a straight line between the two poles, being the shortest between them, and the rays will then form curves between the poles until, by reason of increasing distance, they are no longer influenced by one another, without a better medium of conduction be interposed in their circuit.

"It is natural to suppose that all parts of the earth are not of one uniform density; if so, then some parts are positive, and others negative. Then from this it is easy to see that some of the electricity flowing from the positive pole is the means of restoring equilibrium to negative portions of the earth-not necessarily rendered so

by the negative pole of the battery; and also positive portions, for the same reason, rendered neutral or negative.

"These rays of electricity may be collected in a certain quantity between the point whence they start, and where they are rendered neutral, and by the interposition of a metallic medium that shall offer less resistance than the water or earth -obviously the nearer the battery the greater the chance of collecting them. I do not anticipate the distance of twenty miles is at all too much (with the means we can use to compensate it) to collect a sufficient quantity of current to be useful for telegraphic purposes. Still, the quantity would be small, and with the present telegraphic instruments would not be detected at all. The current in the wire (of the instrument used) must be detected-not by its amount, but that it exists in any quantity, however small. If, then, electricity can be collected in France, simultaneously with a discharge from a battery in England, all that is required is, to find out what to do with it, so that it shall indicate its presence. "I will now lay before you the arrangement I propose for carrying out this design.

"No. 1.-Upon one shore I propose to have a battery that shall discharge its electricity into the earth or sea, having a distance of some five, ten, or perhaps twenty miles-as the case may bebetween the poles.